1. Field of the Invention
This invention relates principally to a speaker device mounted in a vehicle, specifically on the headrest of a seat.
2. Description of the Prior Art
For the stereo replay it is ideal that the distance between the two speakers S.sub.1 and S.sub.2 (FIG. 8) and the distances between each of the speakers and the listeners position L are all equal and that the listeners position is on the frontal axis of the speakers, i.e. that they are located at the three vertices of an equilateral triangle.
However, in car audio devices proposed heretofore, speakers have been mounted often either on the rear deck or on the rear doors, as shown in FIG. 9(A), or two on the front doors and two on the rear deck, as shown in FIG. 9(B). By this reason, when one listens music at a high power in a vehicle, the small space of the vehicle is filled with sounds, and when one listens to music at a low power, sounds are lost in engine noise or noises from the outside. In the case where the two speakers S.sub.1 and S.sub.2 are mounted at the rear part as shown in FIG. 9(A) then, due to the difference in sound intensity between the front and rear seats, sound intensity which is comfortable to those in the front seat can be so high for the rear seat that it is annoying for the listeners (passengers in the rear seat). In the four speaker system shown in FIG. 9(B), where 2 speakers S.sub.3, S.sub.4 are mounted also at the front, although the above-mentioned disadvantages of the two speaker system are eliminated, it has a disadvantage that the location of every passenger is deviated from the ideal listeners position for the stereo replay, which ideal position is the hatched region almost at the center of the interior of the vehicle. From the point of view of the intensity balance, it is not possible that all the passengers have an ideal sound intensity. Furthermore, there is another disadvantage in that sound pressure is lowered in the middle and high sound regions, because the direction of the seats does not coincide with the directivity of the speakers.
In order to realize an ideal audio space in the interior of a vehicle, which has many restrictions, the applicant of this invention has already proposed a headrest speaker device, in which speaker mounting brackets are fitted to the headrest supporting arm disposed on the seat and speaker cabinets are mounted pivotally at both the sides of the headrest by means of these brackets (published Japanese Application No. 57-133188).